This project is currently focusing on gender differences in vocal communication in adulthood and during development, and on the role of individual experience in the acquisition of adult vocal skills. Major findings this year were: 1. Calling rate of infant common marmosets in the context of social separation shows a systematic decline from birth to 3 months, then stabilizes over subsequent monthly assessments. Comparison of vocal behavior in age-matched infants tested in their home colony room and separated from close-range auditory input from the colony indicates that neonates call less, and older (4-6 month) infants call more, when they are in close audible contact with family members and other familiar conspecifics. 2. The vocal behavior of adult male squirrel monkeys living in same-sex social groups was quantitatively assessed for the first time. Males engage in "conversational communication," previously considered to be an exclusively female attribute. However, the incidence of conversational communication in adult males is significantly less than it is in adult females. We currently interpret this gender difference as attributable, at least in part, to early developmental differences in behavioral predispositions between male and female infants.